Process for the digestion of industrial wastes



Feb. 4, 1936. A, M. BUSWELL Er A1.. 2,029,702

PROCESS FOR THE DIGESTION OF INDUSTRIAL WASTES Filed Jan. 2, 1932 MAL',

Patented Feb. 4, 19.."6 K- UNITED STATE PROCESS FOR 'THE DIGESTION OFINDUSTRIAL WASTES Arthur M. Buswell and Clair S. Boruff, Urbana, Ill.

Application January Z3, 1932, Serial No. 588,490

3 Claims.

'I'he present invention relates to a process for treating strong organicwastes such as the in-V readily be seen from the fact that a singledistillery producing solvents by the butyl-acetonic fermentation,produces distillery slop equivalent in quantity, solid matter, and B. O.D. (biological oxygen demand), to the domestic sewage of a city having apopulation of a million. Likewise the wastes from a single creamery in atown of 1500 may contribute 10 to 15 times the organic load from allother sources. 'I'he permanganate oxygen demand of undiluted skim milk,whey and buttermilk waste is from 200 to 400 times that of normalsewage. When diluted with the normal amount of wash and condenser watersit is usually about 25 times as strong as sewage.

Various methods have been proposed for treating such wastes, but uptothe present time, none of these have been found economical.

In summary, the prior art indicates that distillery, creamery, andsimilar wastes containing a high concentration of soluble organicmaterial cannot be fermented anaerobically without previously beinghighly diluted. Of course, it will be understood by those skilled in the-,art that the term soluble organic material and similar terms usedherein and in the appended claims. refer to material in colloidalsolution as well as in true solution.

The surprising discovery has now been made that if the rate of feedingand the detention period are regulated according to the principles to behereafter described, and especially if the digestion is carried out bymeans of thermophilic bacteria, extremely active digestion of undilutedstrong organic wastes may be obtained. By following the process to behereafter described the diculties previously encountered in thedigestion of strong organic wastes, particularly undue acid formation,are eliminated and large yields of valuable fuel gas (methane and carbondioxide) are obtained. According to this process, both the suspended anddissolved organic matter are digested and there is obtained a stabilizedsludge and an eiliuent sufficiently stable to be run to the sewerwithout danger of overloading the treatment works. That the digestion ofthe dissolved organic matter in the present process constitutes a markedadvantage over the prior That .the disposal of these wastes presents aserious problem mayl art processes may readily be seen from the factthat in certain industrial wastes such as creamery wastes, from to 95%of the organic matter is in true solution. Further advantage of thepresent invention will be seen from the following description.

The present process is essentially an anaerobic digestion similar to thewell known treatment of sewage in septic tanks, the outstanding dif--ferences being the adjusted rate of feeding which is employed, therecirculation to prevent acid accumulation, and the high ra tes ofdigestion and gas production secured.' According to this process, ratesof gas prod. ction are possible which are many times the rat^spreviously obtained,- even in the thermophilic digestion of domesticsewage. According to the present process, as much as seven liters of gasper liter of tank volume per day may be produced, in contrast with themaximum rate of gas production of only 1.2 liters reported byHeukelekian and Rudolfs (Sewage Works J., 3, 3, 1931) for thethermophilic digestion of sewage solids.

The process may be carried out in any of the well known types ofanaerobic digestion apparatus such as the septic tanks or other tankspreviously used for sewage sludge digestion. A suit'- able tank for thispurpose is a vertical flow tank comprising a concrete tank with slopingbottom in which the inflow pipeforms a heating coil which discharges theraw waste some distance below the surface but not low enough to disturbthe settled sludge by the current of inflowing liquid. Such a tank maybefitted with suitable means for removing sludge and effluent and meansfor collecting the gas given off during the digestion.

In starting operation anaerobic organisms, of the type which form, asfinal products, gas but substantially little acid, must first be placedin the tank. These organisms may be obtained from any of the knownsources of such organisms and pure cultures may be used vif desired.However, it is preferred to use the following convenient method forbuilding up the desired inoculum.

For example when not industrial wastes such as distillery wastes orcreamery wastes are to be utilized and the digestion is to be effectedby means of thermophilic bacteria, the inoculum may be built up asfollows: Digesting sewage sludge or other suitable starting material isadded to a tank filled with sewage or other liquor which is maintainedat a temperature of 51-53" C. This tank is fed from time to time withraw sewage, sewage sludge, or other suitable material. Afterdecomposition s established, the rate of feeding is regulated inaccordance with the rate of gasV formaa suitable inoculurno'f i tion andacid accumulation, and the digestion is continued with constant feedinguntil rapid digestion is established. At the end of this period,distillery slop, creamery waste, or whatever material is to be digestedis fed instead of sewage,

. or the contents of the tank may be used to inoculate other digestiontanks to which the waste is to 'be fed.

Since the temperature of industrial wastes such as distillery wastes isabove that at which the rounding atmosphere, will maintain the contents'of the' digestion tank at 51-53 C.

The optimum detention period will depend upon the degree of digestiondesired, the solid content of the waste, and the rate of gas productiondesired. For example, when using butyl-acetonic` slop containing 25-40grams of solid per liter, it is preferred to employ detention periodsfrom approximately two days to approximately six days. l

vIn most cases from 1 to 20 days will be found tojbe aJ satisfactorydetention period and where thermophilic digestion is employed from 1 to10 days will be found to be eminently suitable. In any case, the optimumrate of feeding or the optimum detention period for a particular waste yTur.: I Analysis of butyl-'acetonic slop nH 4.5 to 5.3. Total solids,grams per literT 28 to 40. Volatile metter, grams er liter 26 to 36.Volatile acids (as acetic .grams per liter.- 1.8 to 2.4. Ammonianitrogen, milligrams er liter 14 to 80.

Total nitrogen, milligrams perl ter- 1,400 to 1,900. B. 0. D., -day,mlllira 17,000.

Oxygen consumed, m ligrams per liter 10,000 to 20,000 Temperatures o!waste as drawn.. to 95 C.

Per cent of total solids.

Ash

Protein (Org. N.X6.25) i.. Fats and nils Total carbohydrates (lesscellulose) as glucose... Undetermined (crude ber, etc.)

Example I TABLE II Gas production data and for the particularl purposeof itsl treatment Yield of Amysis of gul may readily be determlned byone skllled in the l gas (No. of

Detentlon period vols. per art. tank vol. CH4 C0, B t u The inventionmay best be illustrated by the Per day) Per mi D 00m following specificexamples. In all of these examples the inocula for the digestions werepre- Z421 55 43 l600 pared from raw sewage and sludge as described 4f 25g 40 580 above. The butyl-acetonic slop .utilized in Ex- Y 3- 0, 5s 4.0580 ample I had the approximate composition illus- A mated in Table L lCombine 0.1 0.5 percent H, and 1.0 to 3.0 per cent N'.

Tum III Sanitary ckztal From tankZtimes vol- From tank 4 times vol- Fromtank 6 times volume of waste (B-day urne of waste (4-day ume of waste(-day capacity) capacity) capacity) Original I,

ercent of organic Percent ot organic Percent of o nie b'ggp mattergesied metter gasied matter gas ed Sludge Liquor Sludge Liquor SludgeLiquor p11...- 5. o e. o 7. s 7. e 1.a 8.2 vs. o Total solids, mg.perliter 33, 000 45, 000 5, Dill 40, 000 4. 000 35, 000 4. (1)0 Totalvolatile solids, mg. er liter 30, 000 39, 000 4, m0 33, 000 3, 28, 0003, 230 Settleablc solids, mg. per iter 650 255 200 Volatile acids, asacetic, mg. per liter 2, 000 2, 000 2, 000 l, 000 1, 000 300 500 Ammonianitrogen, mg. per liter-. 50 050 650 850 600 750 000 Total nitrogen, mg.per liter 1, 600 3, 000 1, 000 3, 000 1, 000 3, 000 850 Oxygen consumed,nig. per liter. 16,000 10,000 3,000 l, 300 1,000 Immediate (S0-min.) 01demand, mg per 12 l5 Zi B. O. D., 5-dcy mg. per liter 17,000 7,900 5,700 4, 600 3, 700 3, m0 3, m0 B. O. D., l-day mg. per liter 6,000 2,4001,800 1,500 l, 500 1,000 1,1110 l-day B. O. D., mg. of OI per liter perpercent of volatile matter 2, 000 615 454 cc. gas per gm. volatilematter in 24 hrs 44 ce. gas per gm. volatile matter in 10 days 148 83Percent moisture of sludge after draining 8 hours 70 80 Percent cisludge after drying 3 days 61 Odor as drawn.- Bad Odor after 3 da s.Moderate Volumes oi slu ge drawn per volumes o! waste z;

l Average representative analysis.

Example II An equal'mixture of undiluted buttermilk and whey waste wasdigested at a temperature of 24-,27 C. for a period of 30 days utilizingtwo digestion vessels through which the waste was fed in series. ployedwas one-twentieth the volume of the first digestion vessel per day. Thedata for this digestion are reported in Table IV.

The average rate of feeding em- TABLE IV The anaerobic-mesophilcfermentation of creamery waste (Z4-27 C.)

n Tank Nl (il) liters vol.) Tank N2 (3.5 liters vol.) Waste le per dayAverage gas per day Average gas per day Time-days A I lAnalysis AnalysisVolume, Weight Volume Weight, c c Grams liters grams G0I CH. litersgrams C()I CH (percent) (percent) (percent) (percent) It is known thatattempts have been made to ferment distillery wastes with thermophilicmicroorganisms for the production of volatile acids. However, suchprocesses are contrary to the purpose of the present invention, and anintegral part of the present invention comprises a method for preventingthe accumulating of substantial amounts of volatile acids.

It has been found that at times, especially when a tank is first putinto operation using an industrial waste instead of sewage, there is atendency for the free and combined volatile acids to increase to threeor four parts per thousand (calculated as acetic in accordance with theprocedure described on page 30 of Bulletin 29 of the Illinois StateWater Survey, published May 1930) In such concentrations the buffercapacity of the liquid may be over-taxed and the pH may fall as low as6.0. Addition of lime or other alkaline neutralizing agent will succeedin raising the pH, but the acid content remains high and in some casesis actually increased. Reducing the rate of feed and keeping the tankwell mixed will be found to aid in bringing the tank back to normaloperation.

Also, if all or a part of the overflow liquor from an active tank ispassed through a second tank which contains some contact' material suchas asbestos fiber inoculated with` the proper bac teria, or ripeanaerobic sludge, the acids which may be present in the liquor arereadily converted to gas (methane and carbon dioxide). In such aprocedure, if the first tank starts to develop an abnormal fermentationor the acids increase above three parts per thousand, due to too rapid'feeding or otherwise, some of the liquor from the second tank isrecycled back through the first tank. A more rapid gasification ln thefirst tank results and the acids are reduced much more than can beaccounted for by mere dilution.

An apparatus suitable for carrying out this improved procedure isillustrated diagrammatically in the accompanying drawing. The digester Iis a conical bottom digester of the usual type fitted with a feed linea, an overiiow line b, and a sludge line g. If the digestion is to becarried out by thermophilic bacteria and hot waste liquor is fed to thedigester, the feed line a may form a heating coil as represented in thedrawing. The digester at a point somewhat above the layer of contactmaterial. A feed-back line c connects the two digesters at a point wellabove the ports of the feed lines and is fitted with a pump p suitablefor forcing liquor from the second to the first digester. The seconddigester is fitted with an overflow line f for the final effluent andmay be fitted with a sludge line g, although this is not necessary inall cases. Both digesters are iitted'with gas collecting means of theusual type. The second digester may be considerably smaller than thefirst or it may serve as the second stage for more than one first stagedigester. In the latter case, the lines b and'c may be fitted withvconjoining lines d and e connecting other first stage digesters.

The following procedure may be employed when carrying out the processwith an apparatus of similar line which may be connected to g. The

total volatile acid content of the liquor in digester I is determined atfrequent intervals, and, when it is found to exceed three parts perthousand, the pump p is started and liquor from digester II isrecirculated through digester I until the acid content has again reacheda normal value. During the entire process the gasesY from both digestersmay be collected in the known manner.

It is to be distinctly understood that the above examples are merelyillustrative and areA not to be taken as limiting the scope of thepresent invention. For example, wastes other than those utilized in theexamples may be employed, especially all strong organic wastes such asthose from other fermentations, from starch works, canneries, factories,and the like. The process may also be modified in any way which wouldnaturally occur to one skilled in the art. The invention is likewise notto be limited to any particular type of apparatus, For example, a numberof small tanks in series may be used in place of a large tank as long asthe required detention period is obtained. When extremely accuratecontrol of the volatile acid content is desired it may be found`preferable to use a plurality ot tanks rather than the single seconddigestion tank mentioned above, and in such casesv it may CERTIFICATE oFCORRECTION.

bined volatile organic acid content of the liquid undergoing treatmentbelow three parts by weight calculated as acetic acid per thousandparts'by weight of said liquid.

5 be found desirable to use diilerent types of tanks 2. In a process forthe stabilization of ferment- 5 ln the same series. For example, if highrates able liquid organic wastes having a non-settleof i'eedA areemployed and extremely high rates able solid content substantially inexcess of three giu gas prodtlction reisultitxllier rgiiay be suzh turt;pag-ts byt Wight per ttihousand parts of total liqenceas preven se en aon; anl nsuc u1 was e y a con nuous or semi-continuous lo cases it maybe desirable to use the special types process of anaerobic bacterialdigestion by means of tanks, known to those skilled in the art, which ofmethane-producing bacteria at hydrogen ion are designed to obviate suchdimculties. concentrations suitable for the methane-produc- Tne termvolatile acids" as used herein, desing activity of said bacteria, theimprovement iigxgltj totial) fr?? and combtililiel volatlileie acidsdasvhilh contfipre controlling the rate of feed of l5 e ne y eusua me oslnvovng aci ires was e he digesting waste to maintain l5 caion vitl';la niiilral neig, distillatilomtilndftthe total free andcombinedvolatileorganic acid tra on o e is a e. or exarnp e, e o contentof the liquid undergoing treatment belowing is a suitable method fordetermining total low three parts by weight calculated as aceticvolatile acids in the practice of the present inacid perthousand partsby weight of said liquid.

vention. A sample of digesting waste is allowed 3. In a process for thestabilization of ferment- 20 to settle and 200 ml..oi the supernatantliquid able liquid organic Wastes having a. non-settle `are measuredinto a dlStlllmg ask together Wlth able solid content substantially inexcess of three 131.5111 Cmlent'gxtalllfrl ari-lo'hel mlili'@ parts byweight per thousand parts of total liquid S e a a a m 0 1S Waste by acontinuous or semi-continuous procxgrglletd itnta feceviandjtra-tetdvith ess of anaerobic bacterial digestion by means of 25 a e 0 a V0 a '1e acl C0 en 1S methane-producing bacteria at hydrogen ion concalculatedas acetic acid from the titration value, centratons Suitable for themethane producing assuming a' puclaux recovery factor of 63% foractivity of said bacteria, the improvement which 18150 mldlstmateh b dbed h comprises effecting only partial digestion in a 30 is 'tnilreionflow avm? een esem W a". primary digestion vessel, continuing thedigesl. In a process furthe anaerobic bacterial dimor. m t legit on;tsuceeduc Visel vinding; gestion of i'erinentable liquid organic wasteshavcycfrg, lgts 1 tgtv e o adp eb. gd ssle tu inga non-settleable solidcontent substantially in mam 'am e 0 a ree an com me V0 a' e excess ofthree parts by weight per thousand organic acid Content of the liquid insaid pre- 35 parts of total liquid waste by theaction of meth- CedmgVessel below three parts by weight calcuane-producing bacteria athydrogen ion concenltedislacetc acid per thousand parts by Weighttrations .suitable i'or the methane-producing ac- 0 Sa lqul tivity ofsaid bacteria, the improvement which ARTHUR. M- BUSWELI 40 comprisesmaintaining the total free and com- CLAIR BORUFF- 40 Pai-.ent No.2,029,702. Februaryl 4, 1936.

' ARTHUR M. BUswELL, ETAL.

It is hereby certified that error appearsv n the printed specificationof the above numbered patent requiring Correction as follows: Page lsecond column, line 47, for "not" read hot; and that the said LettersPatent should be read with this correction there'inthat the same mayconform to the record .of the case in the Patent Office. -v

Signed and sealed this-17th day of March., l A. D. 1956.

Leslie" Frazer (Seal) Acting Commissioner of Patents.

control of the volatile acid content is desired it may be found`preferable to use a plurality ot tanks rather than the single seconddigestion tank mentioned above, and in such casesv it may CERTIFICATE oFCORRECTION.

bined volatile organic acid content of the liquid undergoing treatmentbelow three parts by weight calculated as acetic acid per thousandparts'by weight of said liquid.

5 be found desirable to use diilerent types of tanks 2. In a process forthe stabilization of ferment- 5 ln the same series. For example, if highrates able liquid organic wastes having a non-settleof i'eedA areemployed and extremely high rates able solid content substantially inexcess of three giu gas prodtlction reisultitxllier rgiiay be suzh turt;pag-ts byt Wight per ttihousand parts of total liqenceas preven se en aon; anl nsuc u1 was e y a con nuous or semi-continuous lo cases it maybe desirable to use the special types process of anaerobic bacterialdigestion by means of tanks, known to those skilled in the art, which ofmethane-producing bacteria at hydrogen ion are designed to obviate suchdimculties. concentrations suitable for the methane-produc- Tne termvolatile acids" as used herein, desing activity of said bacteria, theimprovement iigxgltj totial) fr?? and combtililiel volatlileie acidsdasvhilh contfipre controlling the rate of feed of l5 e ne y eusua me oslnvovng aci ires was e he digesting waste to maintain l5 caion vitl';la niiilral neig, distillatilomtilndftthe total free andcombinedvolatileorganic acid tra on o e is a e. or exarnp e, e o contentof the liquid undergoing treatment belowing is a suitable method fordetermining total low three parts by weight calculated as aceticvolatile acids in the practice of the present inacid perthousand partsby weight of said liquid.

vention. A sample of digesting waste is allowed 3. In a process for thestabilization of ferment- 20 to settle and 200 ml..oi the supernatantliquid able liquid organic Wastes having a. non-settle `are measuredinto a dlStlllmg ask together Wlth able solid content substantially inexcess of three 131.5111 Cmlent'gxtalllfrl ari-lo'hel mlili'@ parts byweight per thousand parts of total liquid S e a a a m 0 1S Waste by acontinuous or semi-continuous procxgrglletd itnta feceviandjtra-tetdvith ess of anaerobic bacterial digestion by means of 25 a e 0 a V0 a '1e acl C0 en 1S methane-producing bacteria at hydrogen ion concalculatedas acetic acid from the titration value, centratons Suitable for themethane producing assuming a' puclaux recovery factor of 63% foractivity of said bacteria, the improvement which 18150 mldlstmateh b dbed h comprises effecting only partial digestion in a 30 is 'tnilreionflow avm? een esem W a". primary digestion vessel, continuing thedigesl. In a process furthe anaerobic bacterial dimor. m t legit on;tsuceeduc Visel vinding; gestion of i'erinentable liquid organic wasteshavcycfrg, lgts 1 tgtv e o adp eb. gd ssle tu inga non-settleable solidcontent substantially in mam 'am e 0 a ree an com me V0 a' e excess ofthree parts by weight per thousand organic acid Content of the liquid insaid pre- 35 parts of total liquid waste by theaction of meth- CedmgVessel below three parts by weight calcuane-producing bacteria athydrogen ion concenltedislacetc acid per thousand parts by Weighttrations .suitable i'or the methane-producing ac- 0 Sa lqul tivity ofsaid bacteria, the improvement which ARTHUR. M- BUSWELI 40 comprisesmaintaining the total free and com- CLAIR BORUFF- 40 Pai-.ent No.2,029,702. Februaryl 4, 1936.

' ARTHUR M. BUswELL, ETAL.

It is hereby certified that error appearsv n the printed specificationof the above numbered patent requiring Correction as follows: Page lsecond column, line 47, for "not" read hot; and that the said LettersPatent should be read with this correction there'inthat the same mayconform to the record .of the case in the Patent Office. -v

Signed and sealed this-17th day of March., l A. D. 1956.

Leslie" Frazer (Seal) Acting Commissioner of Patents.

